1. Field of the Invention
The present invention relates, generally, to a method for providing a stable quality grade for data services within a packet-switching network and, more specifically, to such a method wherein a quality grade of a transmission is compared with a quality grade demanded by a data service and, depending on a result of the comparison, data packets associated with the data service may be assigned to another quality class.
2. Description of the Prior Art
Say, for example, a subscriber would like to use data services in a packet-switching network; e.g., the Internet. Normally, the subscriber gains access to the packet-switching network by first using his/her subscriber terminal, or a personal computer, to dial into the packet-switching network either directly or indirectly via a private branch exchange or local exchange at an access node. The subscriber then sets up a connection to a network node providing data services in the packet-switching network, e.g. to a computer of a service provider, and requests data services from such a network node by, for example, using an application program available on his personal computer.
Corresponding conditions likewise apply to a private packet-switching network; e.g., to a company network. In this case, the access node to the private packet-switching network is usually integrated into the subscriber terminal or into the private branch exchange. Such a private packet-switching network can also have access to another private or public packet-switching network, such as to a company network or to the Internet. Accordingly, a network node providing data services may be situated not only in the public packet-switching network but also in a private packet-switching network.
In such a packet-switching network, such as the Internet, the data transmission is normally connectionless, i.e. the data packets having identical origin and destination addresses are transported independently of one another, so that neither the order nor delivery of the data packets at the destination node is guaranteed (OSI layer 3 protocol). It is, therefore, also not possible to assure a quality grade for the transmission of data packets between origin and destination nodes, such as a certain bandwidth, delay times, a particular throughput and a low packet loss rate.
Video transmission services (e.g., Video on Demand) and various telephone services (e.g., Voice over IP), in particular, require secure and rapid data transmission on the Internet with an assured constant quality grade. Data services requested by a subscriber, such as Video on Demand, Voice over IP or videoconference circuits require secure and rapid data transmission with an assured and, at the same times stable quality grade.
With respect to the Internet, an approach is currently being discussed within the sphere of the concept of “Differentiated Services”, which guarantees the demanded bandwidth and shorter delay times for transmission of the data packets associated with such data services.
By way of example, an ‘Internet draft’ document “Differentiated Services Model and Definitions” written by K. Nichols and S. Blake, published by the Internet Engineering Task Force in February 1998, proposes a method which permits accelerated transmission of data packets from an origin node to a destination node. For data packets associated with a data service which demands a high transmission bandwidth, particular bits of the ‘TOS byte’ are respectively set in the header part of such data packets. On the basis of the bits which have been set in the TOS byte, the data packets are assigned to different quality classes. Depending on the assigned quality class, the data packets are possibly given preferential treatment in the intermediate nodes. As such, accelerated forwarding, that is to say virtually without delay, to the next intermediate or network node is attempted. An example of a quality class with low priority is the “Best Effort” class customary on the Internet. According to this, the data packets are handled as soon as possible, and as many as possible from one data service are handled. An example of a quality class having very high priority is the “Premium” class, which is distinguished by extremely short delay times and is, therefore, more or less comparable to a virtual connection.
Additional comments relating to the method explained above can be found in other Internet draft documents “An Architecture for Differentiated Services”, written by D. Blake, S. Blake, M. Carlson, E. Davies, Zh. Wang, W. Weiss, published by the Internet Engineering Task Force in May 1998, and “A Framework for Differentiated Services”, written by Y. Bernet, J. Binder, S. Blake, M. Carlson, S. Keshav, E. Davies, B. Ohlman, D. Verma, Zh. Wang, W. Weiss, published by the Internet Engineering Task Force in October 1998.
A significant disadvantage of the method outlined above is that preferential treatment permits data services whose data packets have been assigned to a particular quality class to be assured only of a quality grade which is dependent on the network utilization level.
This problem becomes particularly evident if a large number of data services are requested by subscribers who require a constant or stable and, at the same time, high quality grade for the delay and the transmission bandwidth. In this case, it is no longer possible to provide each data service with the demanded quality grade.
A quite different approach, which has its origin in conjunction with multimedia applications in ATM networks (Asynchronous Transfer Mode), in which virtual connections are set up in a known manner between subscribers and the network nodes providing data services, is to match the transmission bandwidth of multimedia applications to the network utilization level.
For transmission to connectionless packet-switching networks, a publication by I. Busse, B. Deffner and H. Schulzrinne entitled “Dynamic QoS Control of Multimedia Applications based on RTP”, First International Workshop on High Speed Networks and Open Distributed Platforms, St. Petersburg (Russia), June 1995 presents a method in which, for multimedia applications, the transmitter matches the transmission bandwidth dynamically on the basis of the transmission quality obtained at the receiver. In particular, the transmission bandwidth is reduced if, with a high network utilization level, a high packet loss rate at the receiver has been reported to the transmitter. To this end, the ‘RTP/RTCP’ protocol is used, which delivers to the transmitter an acknowledgement about the transmission quality obtained at the receiver.
A significant disadvantage of this method is, accordingly, that such data services cannot be assured of a stable transmission quality for a high network utilization level. Instead of guaranteeing a constant or stable transmission bandwidth, the transmission bandwidth is more readily reduced for a high network utilization level. As such, the data service is received with poor quality. This can even result in data transmission needing to be terminated on account of the quality being too poor for the data service.
An object of the present invention is to develop a method such that, when a requested data service is transmitted, the stable quality grade demanded by the data service is provided.